GNOME Bugzilla – Bug 452782
Image resize sinc / lanczos3 method not working
Last modified: 2008-01-15 14:12:43 UTC
Please describe the problem: There are 4 interpolation types for image resizing : none, linear, bicubic, Sinc/Lanczos3. The last one does not work anymore. Steps to reproduce: 1. Open a photo (say it's 2048x1536) 2. Resize it down to 104x78 with Interpolation 'Sinc/Lanczos3' Actual results: Choosing 'Sinc/Lanczos3' gives similar results to 'none', though not the same. Expected results: I think it should look more like the results given by 'Bicubic' than 'none'. Does this happen every time? Yes Other information: In the beginning of the 2.3 developpement serie, the Lanczos3 interpolation worked like in this release. It worked well in the 2.3.16 release.
Created attachment 91053 [details] comparison of different scaling methods Not sure if I can reproduce it. See attached image, can you tell which method was used for which one?
(In reply to comment #1) > Created an attachment (id=91053) [edit] > comparison of different scaling methods > > Not sure if I can reproduce it. See attached image, can you tell which method > was used for which one? I'd say : top left : original top right : linear or bicubic bottom left : lanczos3 bottom right : none I attached a copy of what I have.
Created attachment 91085 [details] Comparison of scaling method on the 2.3.18-devel release The original image shows "Hello world !" phrase at different sizes.
Additional thought : I've tried scaling up using Lanczos. It seems to give better results than Bicubic. Would it be that Sinc/Lanczos3 algorithm is dedicated at scaling up and bad at scaling down ?
Someone might correct me, but AFAIK the downscaling is still not properly implemented (i.e. the filter kernels are too small) with any interpolation method at all.
This is being handled in bug #166130 already. Closing the report as NOTABUG because the algorithm does work. It is simply not well suited for decimation (downscaling).